Cephalexin (Keflex) During Pregnancy: Is It Safe?

What does the evidence say about cephalexin during pregnancy?

1. In a study of 262 women who took cephalexin during pregnancy, there was no increased chance of birth defects above the general background risk. 1
2. For a bladder infection in pregnancy, cephalexin is commonly dosed at 250 to 500 mg by mouth twice daily for 5 to 7 days, and cephalosporins are a first-line alternative when amoxicillin or ampicillin resistance is a concern. 2
3. Cephalexin works by binding to penicillin-binding proteins and blocking the final step of bacterial cell wall formation, and animal studies found no evidence it impairs fertility or harms a developing fetus. 3
4. Cephalexin passes into breast milk in small amounts and is generally not expected to cause side effects in a breastfed baby; among 20 reported cases of breastfed infants exposed to it, 4 had diarrhea and one had a rash attributed to sensitivity. 4
5. The same 262-woman study found no increase in miscarriage compared with a similar group who didn't take cephalexin, though a separate study reported a higher miscarriage rate among cephalexin users with the cause left unclear. 1

Is cephalexin safe in each trimester?

• First trimester. If a urine culture flags bacteria or you develop bladder-infection symptoms in the first trimester, cephalexin is one of the antibiotics commonly used, typically 250 to 500 mg by mouth twice daily for 5 to 7 days.
• Second trimester. A kidney infection (pyelonephritis) most often develops in the second trimester, which is part of why prompt antibiotic use for a bladder infection matters. Cephalosporins like cephalexin are a common alternative when amoxicillin or ampicillin resistance is a concern for the bacteria involved.
• Third trimester. If you've had a recurrent UTI, your provider may keep you on a lower daily suppressive dose of cephalexin, 250 to 500 mg once a day, through the rest of pregnancy. Small amounts pass into breast milk after delivery, so mention your breastfeeding plans if you're still taking it.